Slicks

[greggers]

Has anyone fitted 17" slicks on their E30?

I found a good supplier of Touring Car slicks that I have been using on a FWD Alfa for the last couple of years and the grip has been amazing. Now I want to try and get them on the E30 we're building.

Although the sizing of slicks is a bit different to normal tyres, they effectively work out as 235 / 38 / 17, we've had them on 7.5J rims and they'll fit up to 9J.

The rims we'll be going for are likely to be Team Dynamics Pro-Race 1 or 1.2 as they're about the lightest weight wheel that I know of at a sensible(ish) price.

Anyway, does anyone have any thoughts/experience?

Obviously we won't be running slicks without a cage. In my opinion it's bloody dangerous to run slicks without one!

[hazd31]

you must make sure everything else on the car is sound, it will eat parts like wheel bearings for breakfast

[greggers]

Hmm, never had a problem with wheel bearings before, although they're cheap enough to replace (although a PITA)... Might look at having two sets of hubs and trailing arms if durability starts becoming a problem. Brakes seemed to take the biggest hammering that I noticed.

More worried about the diff and suspension...

Am I likely to suffer any rubbing with these wheels/tyres?

[Demlotcrew]

The 90-92' DTM E30 M3's ran a 230 width profile and those cars had extensive arch modifications, its not an easy task and you will have clearance issues on the back but not major, the biggest issue will be the total ride height of the car as the overall diameter of the tyre increases.

[GeoffBob]

I have Dunlop DZ03G 245/40/17 semislicks on the rear of my "E30" . Rims are compomotive 8Jx17ET11. See here.



Ideally, offset should be 24mm. Try fitting an 8J rim with 245mm wide tyre and it will collide with both the suspension arm and damper. Only way to fit an 8J rim was with offset =11mm. This does mean that the bearing will wear faster, which I deal with by means of routine maintenance (my car is track only). A little more than just the arches were modified to get these to fit. I doubt that you’ll get these onto a stock E30 without significant flaring of the arches.

[Demlotcrew]

I have a 9j rim on the rear with an offset of et24 and it clears my coilovers easily.

9j seen here;



I also had an 8j Compomotive et25 again cleared the rear arches easily (i had to add a 15mm spacer) and no clearance issues to the coilover.

Andrew

[GeoffBob]

I have a 9j rim on the rear with an offset of et24 and it clears my coilovers easily.

I also had an 8j Compomotive et25 again cleared the rear arches easily (i had to add a 15mm spacer) and no clearance issues to the coilover.

Andrew, Adding a spacer changes the offset of the rim. A rim with ET=25mm with a 15mm spacer measures the same as a rim with ET=10mm with no spacer

Also, the issue here is specifically with regard to 17" diameter rims with tyres that are actually intended to fit the rim. Skinny rubber on wide rims may win you a bling contest but is of no consequence on the race track. Try fitting 245/40/17 tyres on a 17" diameter rim with ET=24mm and the rubber will collide with the trailing arm and damper. If you don't think I know what I am talking about then check out the detailed measurements of my setup presented in my build thread.

[billgatese30]

Its worth bearing in mind that everyone may be running different rear suspension setups and a coil over damper versus a damper and spring in the stock location will affect the clearance required. I'm not sure what the OP is running, or for that fact, I can't remember what either of you are running Geoff/Andrew for rear damper configurations. Just thought I'd point it out before we start saying what will fit and what won't fit the OP's car.

[GeoffBob]

Greggers,

This isn’t the best photo to illustrate my point, since the ridge/lip that runs along the edge of the trailing arm is in shadow, but it’ll do. With 245/40/17 semislicks on 8Jx17”a ET=11mm Compomotive rims that lip is ~12mm away from the inside face of the tyre. I know this because I inserted a divider into the gap between the two and measured. Given some flex in the tyre wall I personally would not want to push the tyre closer to the trailing arm. With a 235 wide tyre you might get away with a rim with ET=15mm, but I wouldn’t want to try a 245mm wide tyre on that rim.

[GeoffBob]

Its worth bearing in mind that everyone may be running different rear suspension setups and a coil over damper versus a damper and spring in the stock location will affect the clearance required. I'm not sure what the OP is running, or for that fact, I can't remember what either of you are running Geoff/Andrew for rear damper configurations. Just thought I'd point it out before we start saying what will fit and what won't fit the OP's car.

Chris, the issue with wide tyres on 17" rims is (in my experience) that of the distance between the inside face of the rubber and the edge/lip of the trailing arm. This issue will be the same on all E30's regardless of suspension setup since the location of rear hub is fixed in relation to the trailing arm (unless something is bent or the bearings poked), regardless of choice of springs, bushes, dampers etc.

[Demlotcrew]

The reason i fitted a 15mm spacer to the 8j is because it was too inset, i could get away with 15mm track on each side and still have no rubbing issues with a 225 profile tyre.

Im pretty sure you know what you are talking about, im going by facts on my own car. And with regards to stretch VS balloon i know which configuration works well on track. Having such a wide heavy tyre combined with a heavy wheel is also of no consequence on track either!

Toyo R888's have a very wide and angled shoulder and their total width is much larger than any other manufacture of tyres.

Depending on the make of the slick the 230 should go ok!

Andrew

[GeoffBob]

The reason i fitted a 15mm spacer to the 8j is because it was too inset, i could get away with 15mm track on each side and still have no rubbing issues with a 225 profile tyre.

With a 225 on the rim I can well believe you Andrew. I hope that we are on the same page, however, with regard to the fact that the issue here is clearance around the tyre, not the rim. I do not doubt that you can fit 8Jx17" ET25 rim, but wearing 245/40/17 Dunlop Direzza semislicks (as is my experience) you will run into issues. Keep in mind that a 245 has ~10mm more either side over a 225mm wide tyre. I therefore stand by my original statement with regard to my 245/40/17 semislicks on 8Jx17" Compomotive rims in response to the OP's request "does anyone have any thoughts/experience?" I feel that I have also presented a reasonable amount of supporting information to back up my statement.

As for the issue of skinny vs wide tyres, this has been debated ad infinitum elsewhere and I see no reason to fuel this fire in order to distract from the original topic. If this is a concern then I suggest downloading Brian Beckman’s series of articles on the physics of racing (see this thread here) where he deals with this matter effectively. Additional un-sprung weight is unfortunately the price to pay for a larger contact patch (due to both larger rolling radius and wider tyre) and must be evaluated upon any track car as a function of the required traction. I will not deny that hp is a very important factor to consider when choosing between the lesser of these two evils. If a smaller contact patch (supported by a lighter tyre and rim) demonstrates the required traction for a proposed application then I would not hesitate to recommend choosing the lighter tyre and rim over the heavier.

[greggers]

Cheers for all of the responses guys. By the time slicks are on the cards the suspension will be on full coilovers.

There's certainly some food for thought in this thread already.

I have no problem with making arch modifications, the limiting factor looks to be the suspension arms, which obviously you can't move out of the way. I don't really want to run spacers, I'd rather just have the right offset on the wheels. Has anyone gone lower than ET10?

If anyone wants to see the tyres, Google Touring Car Spares... At £150 a set you can see why I want to fit them, when R888s are about £80/£90 a piece.

[Demlotcrew]

Why dont you want to run spacers?

I took some photos last night, this is a 9j rim which is almost exactly 10" wide! To the arm i measured about 23mm and i couldnt be "axed" to jack the rear up to check the clearance to the damper/spring, i would have less than most as im running +ve eccentric top mounts on the rear.





The way i see it, thats plenty of clearance!

[greggers]

Why dont you want to run spacers?

I took some photos last night, this is a 9j rim which is almost exactly 10" wide! To the arm i measured about 23mm and i couldnt be "axed" to jack the rear up to check the clearance to the damper/spring, i would have less than most as im running +ve eccentric top mounts on the rear.

The way i see it, thats plenty of clearance!

With spacers, it's either longer bolts or more bolts depending on their thickness, my own logic (rightly or wrongly) tells me that I'd be adding a weakness into the equation. If I'm having the wheels made, I might as well have them made with the offset I need. This does mean I have to get the offset right the first time (or it becomes expensive).

The only problem is, if I go too low on the offset I will have no way to bring the wheels in (unless I have the centres machined - not adviseable), but if I hedge a little with a bigger offset I can always use spacers to push them out.

[Demlotcrew]

I wouldn't worry about it, BMW BTCC cars use really long studs and very light spacers (probably combined still lighter than the metal used on the alloy wheel).



Ive used TCS a few times now, they are good bunch! Only problem is the rolling dia of these wheels is 610mm and the stock E30 wheel should be around the 605 and i really like a dia of 590 as that seems to work best all round.

Its very tempting to try a set! I could get a new set of wheels and tyres for less than im paying for my Khumo V700's

[greggers]

I wouldn't worry about it, BMW BTCC cars use really long studs and very light spacers (probably combined still lighter than the metal used on the alloy wheel).



Ive used TCS a few times now, they are good bunch! Only problem is the rolling dia of these wheels is 610mm and the stock E30 wheel should be around the 605 and i really like a dia of 590 as that seems to work best all round.

Its very tempting to try a set! I could get a new set of wheels and tyres for less than im paying for my Khumo V700's

Indeed they are, last time I went down there he threw in an extra set of 4 for free. Truth be told, with the diff we've got at the moment a bigger rolling daimeter is going to help us.

Depending on where you are I've got a set you could try for size... Saying that, I'd bet you could punt them on ebay and make more than you paid for them. I think the set I have kicking around at the moment came off the BMW!

[kimbo]

Remember peeps, before investing heavily in 17" rims, that BTCC is moving away from 17" rims, starting this year (2011 season) and will be 100% off them by 2013, when all cars will (should) be to NGTC regs, running 18" rims.
In the meantime, go for it! Keep an eye on front lower balljoints, that was the favourite failure we used to have when running sticky tyres on 'stock' suspension components.
Kim

[billgatese30]

I think the clio cup runs 20/62/17 slicks which gives a slighty larger rolling diameter than the BTCC slicks (620mm versus 610) and are slightly narrower (200 versus 230) but it does allow you to keep your options open. Plus the narrower width may help prevent any clearance issues.