'79 244 - Need help to calculate wheel/tyre widths

FrankCsapo

Hey guys,

I need some help with calculating what wheel dimensions I can fit in the guards of my 244. I am going for fully customised 2-piece Work wheels. I am running DVS GAZ coilovers up front and an R brake conversion. Rear has Koni yellows and lowered King springs.

Current wheel and tyre package is 15"x7" ET25 rims with 205/55/15 tyres.

Below are my fender/guard measurements (yes I know the car is slightly lopsided).

I am going for a staggered fitment with the widest possible rear tyre. I need someone to sanity check what I'm thinking. My proposed fitment is:

Rear: 18"x9" ET0 wheels with 255/40/18 tyres.

Front: 18"x7.5" ET25 wheels with 225/45/18 tyres.

Appreciate any insight!

Spac

I had 17x9s with 235/35(?) rear tyres on one of my GTs, and it would still scrape fairly regularly despite a lot of time spent folding back the guard lips and playing with spacer widths.

Don’t forget that the panhard rod pushes the diff sideways as the suspension compresses, so you need a fair bit more clearance than it might seem.

I am pretty convinced that many people speak shit about wheel/tyre fitment.

FrankCsapo

What offset were those 17x9's?

I'm thinking 255 wide on the rear is adventurous as I've found next to nobody doing the same, but very rarely that anyone runs ET0. Do you know how far sideways the diff gets pushed, roughly? With my proposed setup I'm leaving ~10mm clearance each side and the car's already quite low so there's not a lot of suspension travel.

Spac

FrankCsapo
What offset were those 17x9's?
I'm thinking 255 wide on the rear is adventurous as I've found next to nobody doing the same, but very rarely that anyone runs ET0. Do you know how far sideways the diff gets pushed, roughly? With my proposed setup I'm leaving ~10mm clearance each side and the car's already quite low so there's not a lot of suspension travel.

I can’t remember… the info might be on these forums somewhere. The previous owner’s name was Dallas, which is probably your most useful search term.

I am pretty sure that I got it to the point where one tyre would occasionally rub on outside and rarely on the inside, and the other was the opposite.

I do have a reasonably steep/sharp driveway that demands lowered cars to approach on an angle, which really highlighted the rubbing - but it would still rub on normal driving.

GingerNinja

I'm not sure about the rears but I have tested my 16x8.5" ET-2 on the front of my 245 also with GAZ coilovers. They tyres on them are 225/55/16 so not very wide but they're getting tight to the coilover on the inside. Not the spring perch but the tube part. Maybe 10-15mm but I'd have to check.

I'm pretty confident your wheel offset on the front will need to be closer to zero.

There are some threads on Turbobricks with autocross blokes trying to get big rear tyres under there. I've seen a lot of 9" with 255 and such but there was a lot of work to move metal out of the way.

FrankCsapo

Interesting you've got such a fitment on the front with an ET2 offset. If I take my front passenger side measurement as an example, I've got 141mm of space inboard (inset) from the wheel mounting surface to the coilover, and 92mm outboard (poke) to the guard. Assuming the room in the guards is roughly the same between yours and my car, your 225 wide tyre with an ET2 offset means it'd sit 114.5mm inset and 110.5mm poke. This means it will foul on the guard as we've only got 92mm to play with and we're trying to fit 110.5mm in there. How did you manage that?

That's where an ET25 offset would be better, you could then get 137.5mm inset and 87.5mm poke, which would clear the 141mm and 92mm clearances respectively (though it'd be pretty flush).

GingerNinja

FrankCsapo
Interesting you've got such a fitment on the front with an ET2 offset. If I take my front passenger side measurement as an example, I've got 141mm of space inboard (inset) from the wheel mounting surface to the coilover, and 92mm outboard (poke) to the guard. Assuming the room in the guards is roughly the same between yours and my car, your 225 wide tyre with an ET2 offset means it'd sit 114.5mm inset and 110.5mm poke. This means it will foul on the guard as we've only got 92mm to play with and we're trying to fit 110.5mm in there. How did you manage that?
That's where an ET25 offset would be better, you could then get 137.5mm inset and 87.5mm poke, which would clear the 141mm and 92mm clearances respectively (though it'd be pretty flush).

My usual daily wheels on the front are 16 x 8" ET5 with a 215/55/16. Loads of room but I've rolled the fender so it doesn't rub. It will rub if you don't. I was interested in filling in the gap to the front fender a bit more so I threw my 8.5" rears on the front to see if it would work. Big ole baggy 225/55/16 on the 8.5" wheels now but I'll get square 225/50/16 all round for my next tyres.

Search for Hackster's LSA swap thread on turbobricks. This is having a proper go with 18 x 10"

https://i.imgur.com/YSAfqClh.jpg

Dauntless

Hey Frank, are you accounting for your camber angle on the front? I assume you are, but I don't think you specifically mentioned it. Even a couple of degrees can increase guard clearance by 10mm or more.

FrankCsapo

I used a straightedge from the mounting surface of the rotor/hub to measure my clearances, I assume this should take into account my camber angles as there is zero sag from the coilovers when the car is jacked up. Or is there some other method I should be using?

Dauntless

That sounds like the logical way to go about it. When you say zero sag, does that mean you have zero down travel from static ride height? I'd be inclined to put a jack under the control arm as far outwards as you can to ensure the wheel is as close to ride height as possible.

My 15x7 +20 Simmons with 215/60R15s definitely sit inside the guard lip. Compared to those, you'd have the same guard clearance and a slightly shorter tyre. I know your car is lower and 18s have a squarer sidewall profile, but I'd still be surprised if you couldn't get away with a bit less offset on the front.

Special wheel fitment tools do exist, I'm not sure if it'd be worth trying to track one down as a sanity check?

This is all just thinking out loud, so no idea if it helps you. I'm about as far from an expert as anyone could be.

FrankCsapo

Dauntless
That sounds like the logical way to go about it. When you say zero sag, does that mean you have zero down travel from static ride height? I'd be inclined to put a jack under the control arm as far outwards as you can to ensure the wheel is as close to ride height as possible.
My 15x7 +20 Simmons with 215/60R15s definitely sit inside the guard lip. Compared to those, you'd have the same guard clearance and a slightly shorter tyre. I know your car is lower and 18s have a squarer sidewall profile, but I'd still be surprised if you couldn't get away with a bit less offset on the front.
Special wheel fitment tools do exist, I'm not sure if it'd be worth trying to track one down as a sanity check?
This is all just thinking out loud, so no idea if it helps you. I'm about as far from an expert as anyone could be.

Yes by zero sag I mean zero down travel. I jack from the crossmember and the moment the car lifts, the wheels come off the ground.

Given your setup yes I could go a little less offset on the front, but the maximum tyre I'm after up front is 225, so I should have a bit of room to play with. My BMW 135i has 215's up front and they're more than adequate.

I have seen a few tyre fitment tools, namely the Percy's Wheelrite (and other derivatives) but they're impossible to find, or they need to be made in the USA and sent over, which I don't have the patience for.

@timbo ,

Yes, I've already rolled the rear guards and if it needs it I'm OK with cutting metal to make things fit, but if I can avoid it it would be preferable.

I've spent hours on willtheyfit.com using the exact measurement tool you've shown, but I've hit a couple snags with using it:

It doesn't take into account tyre width, only wheel width. Changing the tyre width parameters does not change the inset/poke values. Only changing wheel width does that.The wheel width measurement is bead seat to bead seat as is normal, not actual physical width. The wheel rim edge on each side can be 10mm or more (depending on the wheel) which could mean up to an extra 20mm+ real-world wheel width that the calculator doesn't account for.

So this is why I'm basing my calculations off the tyre I'm trying to fit rather than the wheel width, because the tyre can be wider than the wheel.

timbo

When you're pushing the limits of wheel fitment every millimetre counts. Are you willing to roll your guards and also cut out the rear fenders for clearance?

Its helpful to compare the desired wheel and tyre specs to the existing setup using www.willtheyfit.com

One of the issues with going to 18" wheels will be the increased overall diameter compared to the 15" wheels which would contribute to scrubbing

FrankCsapo

GingerNinja
https://ozvolvo.org/discussion/comment/207104#Comment_207104
My usual daily wheels on the front are 16 x 8" ET5 with a 215/55/16. Loads of room but I've rolled the fender so it doesn't rub. It will rub if you don't. I was interested in filling in the gap to the front fender a bit more so I threw my 8.5" rears on the front to see if it would work. Big ole baggy 225/55/16 on the 8.5" wheels now but I'll get square 225/50/16 all round for my next tyres.
https://cdn.ozvolvo.org/uploads/7DBMMZFWSXJM/20210926-170329.jpg
https://cdn.ozvolvo.org/uploads/TOB2S9SQ68ZN/20210926-170314.jpg
Search for Hackster's LSA swap thread on turbobricks. This is having a proper go with 18 x 10"
https://i.imgur.com/YSAfqClh.jpg

When you say you rolled the fenders do you just mean rolling the inner lip? Or do you mean pulling the fenders out as well? I've got the inner lips rolled already.

Good to see you've fit 8.5" ET2 wheels on the front with success, that gives me some confidence that I can manage the same width, albeit with 18's.

Hackster's setup is incredible. Maybe for the next project car I'll try for that.

VolvoHordz
I am curious about the tyre size choices. They are quite a bit taller overall than you currently have and v's stock. Will give the car a 26.5mm lift.
Taller tyres means more challenges to make them fit. 35 profile tyres would be a better match to stock with the difference in height between and rear smaller than I think you would see by eye.
Another approach to measuring would be to compare clearance of existing tyres to proposed tyres e.g. for the front take closest current point of tyre to strut and measure up 26.5mm and 10mm across towards the strut.
Looking at my own car, I think strut tube clearance should be ok but depending on spring seat height, that could be an issue.
You might be safer to go with less offset on the front. Depending on wheel design you can always have them machined for more offset later. Can't go the other way and reduce offset without adding spacers.

They are a bit taller but I need to clear the S60R brakes which means a minimum of 17", and the wheels I'm getting come in 18" as the smallest size, so that's what I need to make fit. The car is excessively low, I'm talking <100mm in places so I could use a bit of a lift as it is.

You're right about the 35 profile, and looking at my BMW I'm thinking that 245/35/18 may be the better choice for the rear which will result in 22mm extra diameter over the 205/55/15's I have there now. I think that should be manageable, the front would be similar also.

I'll explore different offsets on the front as well, the fact GingerNinja has ET2 fitting up front means I should have some room to play with.

VolvoHordz

I am curious about the tyre size choices. They are quite a bit taller overall than you currently have and v's stock. Will give the car a 26.5mm lift.

Taller tyres means more challenges to make them fit. 35 profile tyres would be a better match to stock with the difference in height between and rear smaller than I think you would see by eye.

Another approach to measuring would be to compare clearance of existing tyres to proposed tyres e.g. for the front take closest current point of tyre to strut and measure up 26.5mm and 10mm across towards the strut.

Looking at my own car, I think strut tube clearance should be ok but depending on spring seat height, that could be an issue.

You might be safer to go with less offset on the front. Depending on wheel design you can always have them machined for more offset later. Can't go the other way and reduce offset without adding spacers.

GingerNinja

FrankCsapo
https://ozvolvo.org/discussion/comment/207141#Comment_207141
When you say you rolled the fenders do you just mean rolling the inner lip? Or do you mean pulling the fenders out as well? I've got the inner lips rolled already.
Good to see you've fit 8.5" ET2 wheels on the front with success, that gives me some confidence that I can manage the same width, albeit with 18's.
Hackster's setup is incredible. Maybe for the next project car I'll try for that.
https://ozvolvo.org/discussion/comment/207143#Comment_207143
They are a bit taller but I need to clear the S60R brakes which means a minimum of 17", and the wheels I'm getting come in 18" as the smallest size, so that's what I need to make fit. The car is excessively low, I'm talking <100mm in places so I could use a bit of a lift as it is.
You're right about the 35 profile, and looking at my BMW I'm thinking that 245/35/18 may be the better choice for the rear which will result in 22mm extra diameter over the 205/55/15's I have there now. I think that should be manageable, the front would be similar also.
I'll explore different offsets on the front as well, the fact GingerNinja has ET2 fitting up front means I should have some room to play with.

I have rolled the thin metal lip flat on the outside but I have not pulled the fender out wider.

FrankCsapo

So my next question - how much minimum clearance between the wheel or tyre to any obstruction (guard, suspension etc) is generally needed? I've seen super flush fits with what looks like only a couple of mm.

I prepared a basic Excel sheet to test for clearances across a variety of tyre widths and offsets, based off the room I have available. Red colours show that configuration will foul, yellow shows there's less than 10mm of clearance.

For the rear, a 245 tyre (8.5" or 9" wheel, doesn't matter as tyre is wider than either) with ET10 will clear everything with at least 10mm space in all dimensions. a 255 tyre will clear most, but leave only 5.5mm against the fender on the passenger side. Would this be enough?

The front is less compliant. Best I can do is a 215 tyre ET25 but still there are <10mm of gap in most dimensions.

A 225 tyre ET27 will technically clear but the clearance is 1.5mm in most dimensions.

So what do you guys think is a minimum "responsible" clearance?

VolvoHordz

The rear definitely needs an adjustable panhard to even things out.

I have done some testing on my 242 as I am also playing around with rims and clearances. With a 225/45R16 on a 7.5" rim with a 18mm offset.

Approx 15mm clearance to the main strut tube body (about 12mm to the support ring for my coilover sleeve).

Approx 12mm clearance to the unmodified fender lip with at a vague guess 2 degrees negative camber. Can't easily check what happens to the clearance when turning and suspension is compressed a bit.

The tyre does rub the inner guard at the front a bit before it reaches full lock. Testing even with a 10mm spacer and it still hits before full lock.

As such, seems like a 18mm offset works pretty well.

FrankCsapo

That's some really good info!

I can't seem to match your results, if I run a 225 tyre with ET18, I will foul the fenders by 7.5mm driver side and 2.5mm passenger side. Are they GAZ coilovers as well? It seems like you have more room in your front arches than I do by a reasonable amount.

My current 205/55/15 ET25 also rub the inner guards at full lock, but if I back it off a tiny bit it's fine. If that's the case with the new wheels and tyres I can live with it. So with your 15mm and 12mm clearances you never foul those areas?

I have an adjustable panhard bar but if I adjust to move the diff to the right (driver side), I am not getting much advantage as it reduces inset room on the passenger side, though 3mm to the right would leave 9.5mm inset and 8.5mm poke on the passenger side (whether that's enough for articulation, I don't know). Leaving it as is but pulling the guards may be better and would give more room fender side to fit a 255 tyre.

I'm thinking if I need to leave a smaller gap anywhere I should do it on the fender (poke) side, as it's easier to pull a guard than to modify suspension.

Dauntless

Would it be worth grabbing a cheap 18x8 5x120 ET40 steel wheel, adaptor and some basic spacers to play around with?

FrankCsapo

I thought of doing something like that and whilst it would give certainty, I'm trying to avoid the outlay. I'm getting some final overall wheel width measurements (not just bead seat to bead seat) from Work Wheels, but while I wait, I think I've got it down to this configuration. If anyone can give this a look over it'd be appreciated.

Front: 18" x 7.5" ET23 wheel with a 215/40/18 tyre.

Rear: 18" x 9" ET10 wheel with a 245/35/18 tyre.

Note the calcs below in the green boxes, the rears should clear all widths inset and poke by at least 10mm (with potential to squeeze a 255 tyre in). The fronts will clear all widths but the poke gaps will be tight, in the case of the front driver side only 2.5mm. I reason that it's better to have more inset clearance as I can't move suspension components, but I can increase poke clearance by pulling guards.

However I think this lack of clearance can be mitigated because the tyres will not be right up into the guard at normal ride height, there will be a vertical space. Both front and rear wheels with tyres have an overall radius of ~314mm. Comparing that to my guard clearances there should be plenty of vertical clearance: 112mm front and 235mm rear which allows for plenty of suspension travel before tyre should touch guard, so the poke gaps may not be an issue as I don't ever expect the suspension to travel that much.