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Going from 15" to 13"... size isn't everything!


RobH72
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Been a busy boy today, after fitting my grill this morning I set about fitting some new wheels....

 

I've been hankering after some 13's for some time and got offered a nice set of Caterham Apollo's (13x6 ET23 front and 13x8 ET23 rear) from a 620R off a mate at a great price. They came shod with some usable Avon ZZR's (185/55 front and 215/55 rear) along with a spare set of rears thrown into the deal.

 

I was worried about the fronts fitting over the Westfield Racing 4 Pots with huge 280mm discs but remarkably they went on with a 1-2mm clearance over the caliper.

 

The rears however, although a similar ET23 and the same 8" width as my old 15's, don't fit as easily due to the lower wishbones. A trial fitting today with an assortment of universal 3mm and 5mm spacers showed that a minimum of 11mm was needed to get clearance. With the spacers on they are workable but I'd be happier with a bit more wheel stud (down to 8 turns) so some hubcentric 15mm spacers (give just enough wheel arch clearance) are in the post along with some longer M12x1.5 63mm bolts giving me options on how to fit the spacers. 

 

The front 205 spec cycle wings don't look amazing over the 185's but are passable if you squint a bit 😂. If I don't keep the 15's as a spare set, I'll probably change the wings and stays to get a better fit.

 

I'll be having a look at the ride height over the next week or so as I've lost about 25mm front and 9mm rear

 

20220623_200000.thumb.jpg.bdf1872a52d93a89b1458ba1c5d79e0d.jpg

 

I did a bit of a weigh in on the wheels and tyres because i'm a geek at heart....

 

Fronts (each) - Apollo 13x6 (185/55 ZZR) 11.6kg vs 16.0kg for the TD 1.2 15x7 (205/50 R1R) 


Rears (each) - Apollo 13x8 (215/55 ZZR) 13.3kg vs 16.6kg for the TD 1.2 15x8 (205/50 R1R)

 

Total rotational/unsprung mass saving of 15.4kg! I'd expected about 10kg looking at wheel weights online so was very suprised and pleased with over 15kg (the Avons must be the difference).

 

As for driving (as that's what really counts!) I was pleasantly surprised by the slightly improved compliance and reduced patter over 15 miles of South Derbyshires cratered roads.

 

I'm impressed with the ZZR's. I was worried about going from 205 to 185 on the front but they give a similar balance and front end grip if not slightly better) but feel more progressive on/past the limit.

 

I'd also say the car is has noticeably improved acceleration, the reduced weight and 3.5% shorter gearing (smaller diameter rear tyre) have definitely made a difference.

 

All in all, quite pleased with the change but time will tell with a bit more mileage under my belt 👍

 

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Good post. As you noted the tyre width has little effect. Compound and type I maintain is much more important than tyre size.

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My car came with 15's and I soon swapped those out for 13's, best thing I have done really. Also went from 205 all round to 185 and much happier. I have since gone a tad narrower at 175 as I like the car to move about under me ( am I normal ? 😄).

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15 hours ago, RobH72 said:

I've lost about 25mm front and 9mm rear

 

This stops me using 13s on the road😏

The loss of front height means the sump guard hitting the road a lot,especially with a passenger in🤦‍♂️

 

How much clearance have you got now to the road?👍

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5 minutes ago, CosKev said:

 

This stops me using 13s on the road😏

The loss of front height means the sump guard hitting the road a lot,especially with a passenger in🤦‍♂️

 

How much clearance have you got now to the road?👍

Since i'm in the garage right now, pushed it out onto the drive and I have 4 inches between sump (already shortened) and ground, thats on 65 profile tyres as well. Planning on going a bit more old school later in the year and swap those for 80 profile, nothing to do with clearence - just looks.

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33 minutes ago, Richard (OldStager) said:

My car came with 15's and I soon swapped those out for 13's, best thing I have done really. Also went from 205 all round to 185 and much happier. I have since gone a tad narrower at 175 as I like the car to move about under me ( am I normal ? 😄).

I remeber that some wizard worked out that any tread over 7" (that show how long ago) were counter productive on the road and only racing tracks could warrent wider sections. Obviously many years have expired (and rubber has taken over the cart wheel steel rim)and apart from straight ones, roads have not improved, so wide wheels are there for show only - discuss. 

I'd love to go to 13" rims but my donor car prevented, meaning 15" minimum for brake clearance.

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1 minute ago, Jim RS said:

I remeber that some wizard worked out that any tread over 7" (that show how long ago) were counter productive on the road and only racing tracks could warrent wider sections. Obviously many years have expired (and rubber has taken over the cart wheel steel rim)and apart from straight ones, roads have not improved, so wide wheels are there for show only - discuss. 

I'd love to go to 13" rims but my donor car prevented, meaning 15" minimum for brake clearance.

I did have to fit 5mm spacers when I got the Cortina replica wheels, as the AP 4 pots were catching a bit. But once done it was fine.

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My front upright assembly is all from a 2wd Cosworth so discs would not fit in the daimeter rims, even at 15" it's tight!

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Ah, ok , with you now. All standard suppield factory stuff here.

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1 hour ago, CosKev said:

 

This stops me using 13s on the road😏

The loss of front height means the sump guard hitting the road a lot,especially with a passenger in🤦‍♂️

 

How much clearance have you got now to the road?👍

 

Indeed, those are some brave ride height losses on a (road going) Mega S2000 unless it was riding particularly high to start with. hat said, those are the Caterham profile tyres, if buying Westfield specific, you could go slightly higher profile and then only tweak the heights a bit.

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1 hour ago, Dave Eastwood (Gadgetman) - Club Chairman said:

 

Indeed, those are some brave ride height losses on a (road going) Mega S2000 unless it was riding particularly high to start with. hat said, those are the Caterham profile tyres, if buying Westfield specific, you could go slightly higher profile and then only tweak the heights a bit.

 

Yes, it's a little low.... I've normally been running about 140mm on the front, I'm down to about 115 ish now! I'll be raising it over the weekend before it sees a speed hump 😂

 

Once I've destroyed the front ZZR's (track day coming up), I'll probably go with a 185/60 (possibly R888R or AR1) to gain back 9-10mm

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Or there's Avon ZZS's too, if you want something just a little less extreme.

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So having 15 inch tyres there must be some benefits surely? I wud of thought having slightly bigger wheels would give better traction under braking as more contact patch, less body roll, Slightly higher gearing which wud be better at say motorway speed.

I used to own a Robin Hood (sorry!)with 13s so hard to compare other than it was a nightmare over speedbumps.

Would love to no a list of pros n cons myself.

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Pros: Bigger brakes, looks, rubber availability (because popular)

Cons Noise, vibration, harshness, expensive rubber, heavy.

 

(I have put the five spokes original 14" wheels on the shelf and fitted 13"  steelies with very pricey 185 vredestein classic tyres.)

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5 minutes ago, Nick Mucklow said:

So having 15 inch tyres there must be some benefits surely? I wud of thought having slightly bigger wheels would give better traction under braking as more contact patch, less body roll, Slightly higher gearing which wud be better at say motorway speed.

I used to own a Robin Hood (sorry!)with 13s so hard to compare other than it was a nightmare over speedbumps.

Would love to no a list of pros n cons myself.

 

It's easy enough to sort the ride height, just added 20mm to the front in 15 minutes with a C-spanner. I'll let it settle and measure up in the morning.

 

Luckily @Ian Kinder (Bagpuss) - Joint Peak District AO posted a load of ground clearance photos a few years ago that I've got in my little archive of useful stuff.

 

On a "seven", lighter is generally better due to being so light weight in the first place, it's what gives us such amazing performance with relatively humble power outputs. 

 

Some people prefer the 15's on the road (and in over 10,000 miles in 2 different 15" shod Westfields I've not had a problem) and 13's on track.

 

Generally, cars get bigger wheels for looks.... Take F1 for instance, all the engineers hate the new 18" wheels, they've made the cars less compliant and slower over a lap with no difference in tyre width. Don't get me wrong though, I'm no Hamilton or Verstappen so the ultimate in performance will definitely not improve my meagre driving skills! 😂

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