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Prevent Mudguards Cracking
Partofthechaos - 2/4/25 at 03:36 PM

A few years ago I remember seeing a recommendation to put something inside the wheelarches to prevent the GRP cracking from stone impacts. However, now I want to find the comment I have no idea where it is! I was thinking of putting on a smear of the thick tar type underseal, does anyone know if this work work? Or any better suggestions?

Thanks,

James

jacko - 2/4/25 at 03:51 PM

I remember that post too
I maybe completely wrong but I think it was under seal painted on I don’t know if it worked
G

Andy W - 2/4/25 at 06:00 PM

I covered the underside with clear silicone

Andy

MikeR - 2/4/25 at 06:56 PM

I've no idea if this works and had thought of doing the same myself (and haven't yet). One thought thats crossed my mind seeing the thread - any extra weight has to be carried by the famously reliable cycle wing brackets.

Partofthechaos - 2/4/25 at 07:03 PM

Yes, that was my thinking. Weight needs to be minimal, also durable and waterproof. Having said that a smear of something has to be beneficial and will be negligible weight.

SteveWalker - 2/4/25 at 07:16 PM

I can't remember what I used, but it was sold specifically for it. It came in a can, was painted on like any other paint and dried as a thick, rubbery layer.

JoelP - 2/4/25 at 08:49 PM

Mine live in the garage and get refitted for the mot, along with the front numberplate. No chance of either getting damaged!

Partofthechaos - 3/4/25 at 05:28 AM

quote:
Originally posted by SteveWalker
I can't remember what I used, but it was sold specifically for it. It came in a can, was painted on like any other paint and dried as a thick, rubbery layer.


That sounds spot on. This is the closest I can find on CBS, does this sound like the stuff you used?

https://www.carbuilder.com/products/bitumastic-rubber-underseal-aerosol?_pos=18&_sid=49dbe7987&_ss=r

nick205 - 3/4/25 at 08:22 AM

On my MK Indy I fitted my front cycle wings as close to the tyres as possible (just about squeeze my fingers in). 3k miles and no cracks.

Rear wings were fixed height determinded by the bodywork. Again 3k miles and no cracks.

Partofthechaos - 3/4/25 at 08:51 AM

OK, that gives me confidence that I may be overly cautious worrying about this aspect. Having said that, currently the arches are off the car so it is an idea time to sort it. I've ordered the stuff from CBS, will see how it goes.

SteveWalker - 3/4/25 at 11:57 AM

quote:
Originally posted by Partofthechaos
quote:
Originally posted by SteveWalker
I can't remember what I used, but it was sold specifically for it. It came in a can, was painted on like any other paint and dried as a thick, rubbery layer.


That sounds spot on. This is the closest I can find on CBS, does this sound like the stuff you used?

https://www.carbuilder.com/products/bitumastic-rubber-underseal-aerosol?_pos=18&_sid=49dbe7987&_ss=r


No. I picked the stuff up at a show and it came in a 1 litre paint can, for brushing on. Once opened, it had to be applied to all four mudguards, then recoated soon after, as the contents of the can would start setting on exposure to air.

This is not the same stuff, but it seems similar in many ways: RubberGuard coating and it does state on the container that it is suitable for wheel arches.

[Edited on 3/4/25 by SteveWalker]

Partofthechaos - 3/4/25 at 12:19 PM

Thanks Steve, I'll look into this one too.

jacko - 3/4/25 at 06:58 PM

Looks like stone guard sprayed on car sills or the rubber guard that is used on pickup load areas

Slater - 4/4/25 at 06:37 PM

I used a cheap camping mat, cut down to fit inside the rear wheel arches, very cheap and very light weight too. Think I used contact adhesive to glue them in.

Is this the post you are refering to?

https://www.locostbuilders.co.uk/viewthread.php?tid=220493

[Edited on 4-4-25 by Slater]

Partofthechaos - 4/4/25 at 07:21 PM

Good idea, I imagine that also cuts down on tyre noise too (not thst really matters).

coyoteboy - 5/4/25 at 09:53 PM

quote:
Originally posted by JoelP
Mine live in the garage and get refitted for the mot, along with the front numberplate. No chance of either getting damaged!


Do you not instantly get pulled especially if out in wet weather? It's a real pedestrian risk too, not sure I could justify that.

JoelP - 6/4/25 at 05:15 AM

Not sure how mud guards affect pedestrians, but I don't usually go out in the rain. There's no roof! If I got pulled I'd just say they snapped. What's the worst that can happen?

coyoteboy - 7/4/25 at 09:02 AM

quote:
Originally posted by JoelP
Not sure how mud guards affect pedestrians, but I don't usually go out in the rain. There's no roof! If I got pulled I'd just say they snapped. What's the worst that can happen?


a) stones getting fired about
b) I guess you've never seen the F1 race where the marshall got clipped by the F1 car and folded/wrapped round the wheel and died then. There's a reason wheel coverings are part of the C&U laws. When you fall onto the top of an uncovered wheel, you get pulled foward and down under the wheel. With a covering you tend to just bounce off.

[Edited on 7/4/2025 by coyoteboy]

MikeR - 8/4/25 at 11:48 AM

Wasn't it snappy / snapper (can't remember his name) who was ex bike cop. Around the early days he admitted to being involved in the SVA creation and answered any questions over silly rules. EG "why do all the edges have to be covered, if i hit someone at 60mph a sharp edge is the least of the worries". Turns out most accidents are low speed therefore a narrow / thin edge could cause a serious laceration. By covering they're reducing the chance of that.

Every rule, whilst it could seem silly had a very sensible justification.

coyoteboy - 8/4/25 at 12:24 PM

Not for the sensitive, very graphic....:
https://www.youtube.com/watch?v=lyAVSHzeZ6Q&pp=ygUTZjEgbWFyc2hhbCBydW4gb3Zlcg%3D%3D

That said, there are C&U laws for not causing road spray also, which apply to all vehicles except tractors/machinery I think.

[Edited on 8/4/2025 by coyoteboy]