New alloys/tyres sizing + center bore size

[ccarty85]

So using previous threads and trying to find out as much info as possible before disturbing you guys with what must be a pretty common thread, here's where I'm at. I'll try and keep this breif...

Current set up - 2018 Seat Leon FR 5f ST running on 7jx17 et49 standard Seat 5 spoke alloys with 225x45x17 tyres.

Looking to buy a 2nd set of complete wheels to run in the summer months (I live in Denmark which means I have a set for winter and a set for summer).

After months of searching, I find myself drawn towards a set of Japan Racing JR18 in hyper grey.

Looking to buy a set of 7.5jx18 et40 which according to willtheyfit.com will have an 'outer poke' of 15.4mm which should be perfect, as I'm currently running 15mm spacers all round, which for me, give a good overall fitment.

Here's a link if anyone is interested -

Alloy Wheel & Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit

Alloy Wheel & tyre fitment calculator - it calculates inset, poke, speedo error, tyre stretch and loads more.

www.willtheyfit.com

My questions. How important is it to find wheels with the exact center bore dimension as the factory rims? Mine should be 57.1mm but I tend to find either 66.6mm or 74.1mm options. Possibly with more searching, I could find an exact match, but some far, no luck.

2nd question. Tyre sizing. Is there something in particular I should be considering here? I've used www.tyresizecalculator.com and think that a set of 225x45 should work fine and are a little more budget friendly that a set of 235x50's.

Any opinions on rim choice, rim size, center bore and tyre size/choice would be much appeciated. To be honest, I've never spent so much money on what's essentially an accessory for a car before, so I'm feeling both a little overwhelmed on choices and a little out of my depth.

Thank you to anyone who might be able offer any guidance.

 

[SRGTD]

My questions. How important is it to find wheels with the exact center bore dimension as the factory rims? Mine should be 57.1mm but I tend to find either 66.6mm or 74.1mm options. Possibly with more searching, I could find an exact match, but some far, no luck.

Firstly, apologies for the rather lengthy post (made lengthy due to the screenshots I‘ve included), but hopefully you’ll find it useful.

Pretty much all aftermarket alloys will have a large-ish centre bore - this is a deliberate action by alloy wheel manufacturers so that their wheels will fit as wide a range of vehicles as possible. It’s not critical that you find wheels with 57.1 centre bore; if you’re buying your wheels new from a reputable alloy wheel retailer then the retailer should supply a fitting kit that includes a set of spigot rings (reducing rings) of the correct size. These fit inside the centre bore of the wheel to reduce the centre bore size to 57.1, which will help centre the new wheels correctly on your car’s wheel hub assemblies.

Also bear in mind that many aftermarket alloys use tapered wheel bolts (I’m pretty certain OEM Seat wheel bolts are radius bolts - also known as conical or round). Be sure to provide make and model details of your car to the alloy wheel retailer so if new bolts are required, they can supply these part of the fitting kit.

2nd question. Tyre sizing. Is there something in particular I should be considering here? I've used www.tyresizecalculator.com and think that a set of 225x45 should work fine and are a little more budget friendly that a set of 235x50's.

One important consideration when changing wheel / tyre size is to ensure the overall rolling radius of the new wheel / tyre set up is as close as possible to the original wheel / tyre set up, so your car’s speedometer reading remains accurate. It’s important to ensure that the speedometer doesn’t display a lower speed than the actual vehicle speed, otherwise the driver could unknowingly exceed any applicable speed limits. With your suggested tyre size of 225/45 R18 for your new wheels, your car’s speedo would under-read by around 4% so at an indicated 100 kph you’d actually be travelling at 104 kph which IMHO is too large a margin of error- see screenshot below;

I think that the size of tyres that Seat fitted to mk3 Leon FR’s with 18“ wheels are 225/40 R18. According to the table below, this is the ideal tyre width for a 7.5J wheel and would be the size I’d choose for your new wheels.

Although your speedometer would be understating the actual speed with 225/40 R18 tyres, the margin of error is less than 0.5%; see screen shots below;

I do really like your choice of wheels - a nice classic design (quite similar to BBS CH-R‘s) and a good colour choice . A 7.5J wheel with an offset of ET40 fitted with a set of 225/40 R18 tyres shouldn’t give you any rubbing or clearance issues either. Be sure to post up some pictures once you’ve got them fitted to your car.

Lastly it would be worth checking whether or not there are any insurance implications in Denmark of fitting new wheels to a your car. In the UK, this is considered to be a modification for insurance purposes which should be notified to the insurance company.

 

[BigJase88]

Yeah the above post mentions everything

225/40/18 are the tyres you want

235 on a 7.5J rim is too wide

225/45 and 235/50 will be much too large diameter wise. The 235/50 will be massive. The profile [40/45/50] is not in mm as many believe, it is a percentage of the width so a 235/50 will have a 117.5mm sidewall height where as a 225/40 will have a 90mm sidewall



Again regarding the larger centre bore. You will be supplied with plastic spigot rings that fit inside the centre bore on the alloy.

Another thing worth mentioning aftermarket alloy wheels generally use taper wheel bolts, your oem seat alloys will be radius bolts. You should get a set of taper wheel bolts with the aftermarket wheels and you will have to use the new taper bolts

 

[RUM4MO]

If you have a spare wheel already in the boot, remember to keep a set of original wheel bolts in with that spare wheel so that you can safely use it if you get a puncture.

I provided my daughter with a set of original wheel bolts that I painted the heads with yellow paint so that she will be able to use the original spare on her Cupra.

I've also found that aftermarket wheel suppliers only use a few lengths of wheel bolts, so expect the supplied bolts to be maybe 5mm longer than the originals, that in itself is not a huge problem, but it means a longer length of "dirty" thread being dragged back through the hub wheel flange threaded holes, so I got her to fund a set of 27mm taper bolts and a set of locking bolts to suit, chemi blackened ones to blend in with the gun metal wheel colour.

Maybe just one of things that father do to try to help their kids!

 

[ccarty85]

First of all, a huge thank you for the time and effort you've spent on the replies. The level of detail, knowledge and help with such informative responses is truely appreciated and way, way more than I ever expected. The first reply from SRGTD just goes above and beyond everything I expected and really clarifies all the questions I had. I really can't thank you enough and it makes me (a complete newbie) far more confident in both my purchase and also that I'm going to do the right thing size-wise. So again, thank you sir for taking the time out of your day to help me, it really is a huge help.

At which point, I didn't think anyone could possibly add to what appeared to be a super detailed and thought out response...but again, I was wrong!

So to you BigJase88, thank you for further explaining tyre size and explaining my need for taper bolts. Certainly without knowing the latter, I would have been stuck!

And finally, RUM4MO, I would have totally forgotten to keep an extra set of original bolts for the spare wheel (again a newbie error!). So although I hope I would never come across the embarrassing problem of being stuck on the side of the road with a perfectly good spare wheel with no means of attaching it to the car, I'm sure, knowing me, I would have learned that lesson the hard way! As a little side note, my daughter is only 4 years old, so I hope I have a little time to accumulate some wisdom and help out in a similar way to how you're doing. Top marks in that respect.

Again, a big thank you from me, now time to part with some hard earned cash! I will update here with photos when I get them on.

Chris

 

[SRGTD]

@ccarty85; you’re very welcome.

Looking forward to seeing the new wheels on your car .

 

[ccarty85]

Sorry to say, I have one more question! I haven't quite pulled the trigger yet, but I have a question regarding suspension strut clearance, or in my case, the possiblity of too much clearance!

So as cleared up in the original post and replies, I will be going for 7.5Jx18 ET40 rims for the front which (according to willtheyfit.com) have the ideal poke of 15.4mm and sit 2.6mm from the suspension strut. However, for the rear, I would like to get some 7.5Jx18 ET35 which will sit flusher with a poke of 20.4mm but sit 7.6mm further from the suspension strut in comparison to the oem rims. Question is, is 7.6mm too much?

Here is a link with my 'before' and 'after' numbers if anyone is interested.

Alloy Wheel & Tyre Fitment Calculator. Offset, Tyre Stretch and Speedo Error | Will They Fit

Alloy Wheel & tyre fitment calculator - it calculates inset, poke, speedo error, tyre stretch and loads more.

www.willtheyfit.com

This really should be the last question, as the summer weather seems to have hit us here in Denmark and I need to change over from the winter wheels+tyres that are currently on!

Thanks

Chris

 

[BigJase88]

They will be fine

 

[ccarty85]

Perfect, thanks Jase

 

[ccarty85]

Time for an update. After so many of you helping me out, the least I can do is put some photos up (technology, don't fail me now!). Ended up getting a great deal on these, but with an ET35 all round inseatd of getting ET40's for the front. Everything lines up well (might opt for some 5mm spacers on the rear) and although it was a tough decision on colour, this is what I went for. Not everyone's cuppa tea I'm sure, but each to their own!

Thanks again for some cracking advice and no doubt, I'll be back again with more questions as the journey continues!

(first image is with standard OEM Seat rims with winter tyres running 15/20mm spacers)

And now...Japan Racing JR18 7.5Jx18 ET35 in hyper grey.