fecking speed bumps!

[neil0205]

This is the 3rd week of owning my beloved cerb.I`m using it daily so I`m either going to be skint in a few weeks or I`ll have a sponsership off optimax (i wish!).With it only having a low ground clearance on 16" wheels i was wondering if this was improved if it sat on 18" ones.Where i live there are a lot of speed bumps to keep the traffic on the main roads,so i`m constantly going over them.Whilst slowly doing this and pulling a stupid face when you hear the sickening scrape from underneath i think of ways of preventing this.Will bigger wheels help or have i got to go and get a hammer and bolster and take the peak off the few hundred local humps!!

[nick cooper]

Dont think 18s will make any diference as they have the same rolling diameter.(i think) so you may have to buy a hammer and chisel, good luck.or try one of these

You could always use it as an excuse to go the long way round

>> Edited by nick cooper on Tuesday 30th May 13:34

[gazzab]

What suspension do you have?
Has it been set 'too low' ?

[grass widow]

Must admit I go the long way round, but when I have gone over bumps I've had no problem, we run 18's don't know if it makes a difference though. Its a good excuse to make a 10 minute journey 30 mins or so.

[alinton]

I rarely have problems with speed humps, at least not after I wound my car back up to the standard height of 130mm ground clearance.

Some people set it lower when fitting Nitron shocks for example, but I think that makes it too low for the mountaineering we often have to do these days.

[kevin63]

I have 16" on my Cerby (18" have the same rolling diameter so will not help)and i live in speed hump city, i have change my shockers to Avo but that is not a cure, all you have to do is crank the rear end up a little, all Cerby's can be done even if it is standard and it is very easy, just do each side the same, i would do it either 5mm or 10mm at a time then try it.

[david smith]

same problem .. Im on 17's .. quite low .. clouted my exhaust last night on raised manhole
... I have a nice rattle to worry about now!! - I only have adjustable rears maybe I need
to spend some more on the fronts ...

DAS

[kevin63]

david smith said:

same problem .. Im on 17's .. quite low .. clouted my exhaust last night on raised manhole ... I have a nice rattle to worry about now!! - I only have adjustable rears maybe I need to spend some more on the fronts ... DAS

You may find that it is only the exhaust touching on the shields, mine did this and all you have to do is put some more 10mm washers in between the chassis and shields.

[marcus1970]

Surely if the diameter is bigger then the car will be slightly higher off the ground. eg 16 wheels means centre of hub will be 8 inches off the floor. 18 inch wheels will mean the centre of the hub will be 9 inches off the floor. Put bigger tyres on and again the centre of the hub should be further away from the floor.

So get 18" and slightly larger tyres should give extra clearance. PS I don't have this problem so I won't do either.
Cheers
MB

[350matt]

Something that helped a lot on mine was fitting de-cat pipes which also meant that I could remove the spacers from under the chassis closing plate which gains another 10-12 mm

Matt

[jensena]

marcus1970 said:

Surely if the diameter is bigger then the car will be slightly higher off the ground. eg 16 wheels means centre of hub will be 8 inches off the floor. 18 inch wheels will mean the centre of the hub will be 9 inches off the floor. Put bigger tyres on and again the centre of the hub should be further away from the floor. So get 18" and slightly larger tyres should give extra clearance. PS I don't have this problem so I won't do either. Cheers

The rolling radius of the tyre will remain the same because.........

Say you have a tyre size of 215/50x16.
This means the tyre is 215 mm wide. The height of the sidewall is 50% of the width of the tyre, and the radius is 16". So in this example....
* The sidewall part of the tyre is 50% of 215mm (=107.5mm).
* Half the radius of the wheel is 8" (=203.2mm)
* From the wheel centre to the ground the measurement would be 107.5 + 203.2 =310.7

If you fit 17" rims, you go for a 215/45x17 tyre. So in this case....

* The sidewall part of the tyre is 45% of 215mm (=96.5mm).
* Half the radius of the wheel is 8.5" (=215.9mm)
* From the wheel centre to the ground the measurement would be 96.5 + 215.9 =312.4

So 17" wheels would give you 1.7mm extra ground clearance.

When you up the wheel size, and keep the same width of tyre you have to go fora lower ratio to keep the same radius. You have to do this otherwise the wheel and tyre radius will be too large, it might not fit the arch and the gearing will be altered affecting performance and speedo readings, .

Phew, my brain hurts now - hope it all makes sense !!

[kevin63]

Well done jensena, i didn't want to get into that one but i think you did ok there.

[marcus1970]

jensena said:

marcus1970 said: Surely if the diameter is bigger then the car will be slightly higher off the ground. eg 16 wheels means centre of hub will be 8 inches off the floor. 18 inch wheels will mean the centre of the hub will be 9 inches off the floor. Put bigger tyres on and again the centre of the hub should be further away from the floor. So get 18" and slightly larger tyres should give extra clearance. PS I don't have this problem so I won't do either. Cheers The rolling radius of the tyre will remain the same because......... Say you have a tyre size of 215/50x16. This means the tyre is 215 mm wide. The height of the sidewall is 50% of the width of the tyre, and the radius is 16". So in this example.... * The sidewall part of the tyre is 50% of 215mm (=107.5mm). * Half the radius of the wheel is 8" (=203.2mm) * From the wheel centre to the ground the measurement would be 107.5 + 203.2 =310.7 If you fit 17" rims, you go for a 215/45x17 tyre. So in this case.... * The sidewall part of the tyre is 45% of 215mm (=96.5mm). * Half the radius of the wheel is 8.5" (=215.9mm) * From the wheel centre to the ground the measurement would be 96.5 + 215.9 =312.4 So 17" wheels would give you 1.7mm extra ground clearance. When you up the wheel size, and keep the same width of tyre you have to go fora lower ratio to keep the same radius. You have to do this otherwise the wheel and tyre radius will be too large, it might not fit the arch and the gearing will be altered affecting performance and speedo readings, . Phew, my brain hurts now - hope it all makes sense !!

I thought the 50 bit meant 50mm extra on the radius (depth of tyre), therefore 100mm on the whole diameter of the wheel. 50% on my 255 would be 127.5 (63.75 radius)for my tyres but they are only about 50mm deep! therefore not sure about the 50% - but am willing to learn as tyres aren't my speciality, in fact I don't really have one!
MB

[jensena]

Marcus, I knew I was right, but just in case you dont believe me, I did a quick 'google' so check these :-)

www.torquecars.co.uk/Tuning/alloy-wheels.php

www.tyres-online.co.uk/techinfo/aspect_ratio.asp