Size does (seem to) matter?

[Pasha]

Having the 7 refurbished at Proline later in the year. Have plans to fit carbon front wings from Ultimate Carbon (thanks for the tip Mr. Wright). Now my 7 has 15" wheels but I don't think it was born with those. (Cue for Colin Heseltine to chip in). 
 

Anyway they sell guards for 13"/14" wheels which I guess would replace what's on the car because, as mentioned, it was born with smaller wheels. I'll get to the question...

The outer diameter of the wheel must be the same regardless of the rim size, otherwise the speedo would be all wrong. So why does it matter that the guards are for specific wheel sizes. 
 

I've probably missed something here. I stand to be corrected. 
 

Paul

[garybee]

That's a reasonable assumption to make but isn't the case.  Even 13" wheels don't necessarily mean you'll have the same rolling circumference because of differences in tyres.  For example my 7 started out on 185/70/13 tyres as that's what was used for the academy at the time.  It now has 185/60/13 tyres fitted which have a much smaller rolling circumference but is fairly normal for track use.

The speedo' is adjustable to compensate.  I just stuck a GPS to the dash and fiddled until they matched.  GPS is very accurate for speed if you pick a straight(ish), level(ish) road.

[SLR No.77]

Historically there's been two sizes of cycle wing (ex-Caterham) for either 13"/14" or 15"/16" wheels, but the radius of the wing is fundamentally the same. The main difference is the length with the 15"/16" cycle wings being much longer to finish closer to the ground at the rear of the wheel. Most people prefer the 13"/14" cycle wings whichever wheel size they're using and it's actually possible to use the smaller wing with 16" HPC wheels!

Stu.

[Pasha]

Thanks guys. The Speedo is accurate and has never been adjusted (didn't know you even could). 

The aspect ratio thing is the first thing I thought of (my 76 Triumph Stag runs 195/70 tyres which are the same as 185 tyres from the era), so I'm pretty sure the OD of the entire wheel is the same as it ever was. I'll likely go with the 13/14" cycle wings (I'm sure that's what's on it currently). The only issue being the propensity to throw stones at the rear wings. I understand now and thank you both. 

Best regards 

Paul

[SLR No.77]

Mudflaps 

[Wrightpayne]

On older cars (like yours) altering the speedo reading involves a change of the drive in the gearbox - I've done mine in situ but its very cramped! Later cars with electronic speedos are programable.

The other point worthy of note is that the wingstays are different depending on the wheel size - there are 3 types. 13/14, 15/16 and 13" race which is v low.

Ian

[Colin Heseltine]

I will chip in.  Although I changed the wingstays, they were identical in size to those fitted when the car was new and had its original 14" wheels.  I have had 13", 14" and 15" wheels on the car with those same stays.

Colin

[Toughie]

#7, Stu,

Mudflaps on a 7!  Never thought of that.

I can't see the flaps very well in that picture, but I can see how polished your wing is.  Has it ever seen the road?

[7 wonders of the world]

Mudflaps  

........massive reduction in 'blat splat' as you pass Welsh farms  

I used this only in black

https://www.ebay.co.uk/p/1045679383

 

[SLR No.77]

Here you go Alan ...

[Mrp]

I did the same on my S3 and didn't have stone guards on the Carbon wings and never had any blat splat or stone damage, about to do the same on my SV

Mrp

[Toughie]

Thanks fr the link 7WOW.  Ordered.

How do you chaps fix them to the arch?

[SLR No.77]

I fixed mine to the stay rather than the cycle wing itself using a couple of threaded Bighead fasteners, the cycle wing was then bonded over the top.

Stu.